Liquid crystal display screens occupy a broad market in the field of portable displays. Consumers are increasingly requiring low power consumption and high resolution in portable visual switches. The display quality of liquid crystal screens is related to the power source voltages of their liquid crystal drive units. Therefore, liquid crystal drive units must have low power consumption, and liquid crystal drive voltages should be symmetrical. Additionally, in order to broaden the practical applicability of liquid crystal drive units, there should be a wide range of options in choosing power source voltages. Liquid crystal drive units need to provide high drive voltages, so in terms of reliability, stability, and cost, power source circuits that produce high voltages are normally integrated into the liquid crystal drive units. Power source circuits include boost circuits that can achieve low electrical consumption levels by using charge pump circuits that boost voltage through the use of charge pumps along with the accompanying control circuits.
When applying DC voltages to the electrodes of a liquid crystal screen, the liquid crystal molecules' reactivity will be reduced, as will the life of the liquid crystal; therefore, AC voltage must be applied to the electrodes of the liquid crystal screen, i.e. constantly reversing voltage applied to the liquid crystal screen's electrodes. However, it must be ensured that the voltage dropouts during the periods before and after reversing are equal; that is, the consistency and symmetry of voltage changes must be ensured.
In most charge pump circuits, the produced voltage is a whole-number multiple of an externally-provided system voltage (in theory), and an appropriate liquid crystal drive voltage cannot be directly produced. A low dropout regulator (LDO) or another structure is further required to regulate the production of stable high voltage for use in driving the liquid crystal. This type of chip may contain a voltage higher than the highest liquid crystal drive voltage, thereby leading to a complex circuit structure and high power consumption. The production of the highest negative driving voltage is also normally performed by first using a charge pump circuit to produce a highest negative voltage, then using a subtractor to produce a smaller negative voltage for use as the highest negative driving voltage for the liquid crystal. Thus the existence in a chip of a negative voltage even greater than the negative liquid crystal driving voltage can also lead to circuit complexity and high energy consumption.
Therefore, it would be desirable to have a type of power source circuit aimed at resolving the problems of circuit structure complexity and high power consumption currently plaguing the generation of liquid crystal driving voltages.